1. Field of the Invention
The present invention relates to image forming apparatuses of the electrophotographic type. In particular, the present invention relates to toner collecting devices of the cyclone separator type that collects toner removed from image bearing members by separating and carrying the toner using swirling airflow.
2. Description of the Related Art
In image forming apparatuses of the electrophotographic type, most toner images formed on photosensitive members or transfer bodies are transferred to recording materials such as recording paper during a transferring step. However, some toner remain on the surface of the photosensitive members or the transfer bodies without being transferred.
To date, such remaining toner have been scraped off using cleaning devices including removing units such as brushes and blades, and carried to collecting boxes by toner collecting devices such as rotating screws. However, such toner collecting devices require screws for carrying the toner and driving sections for driving the screws. This leads to an increase in the size of the devices, and moreover, affects the flexibility of the structure of the image forming apparatuses.
Therefore, a toner carrying device that carries toner using an airflow generated by suction and collects the toner separated from the air using a cyclone separator as shown in FIG. 4 has been discussed in, for example, Japanese Patent Laid-Open Nos. 07-319355 and 11-249522. This toner carrying method using airflow does not require a carrying member for carrying the toner and a driving section for driving the carrying member. Moreover, since an air hose in which the air flows can be freely arranged, the flexibility of the structure of the image forming apparatus can be enhanced, and the size of the apparatus can be advantageously reduced.
Such a toner collecting device includes a cyclone blower 212 for sucking remaining toner via a carrying path (213, 216, 217) after removing the remaining toner using a cleaning member, a cyclone separator 214 collecting the toner at a predetermined position of the carrying path, a toner collecting container 215 disposed under the cyclone separator 214, and a filter 218 disposed in an air intake channel to the cyclone blower 212 or in an air exhaust channel for collecting fine particles of the toner.
The separative power of the cyclone separator 214 of this type largely depends on the wind speed of airflow generated by a suction blower for sucking the air.
In a cyclone separator system, the diameter of separable particles is determined on the basis of the diameter of a cylindrical air intake section and the wind speed of the intake air.
FIG. 2 is a graph illustrating a relationship between the minimum diameter of toner particles that are separable using a cyclone and the radius of the cyclone (radius of gyration of fluid when the fluid is rotated using the cyclone). The abscissa represents the minimum diameter of the particles separable using the cyclone, and the ordinate represents the radius of the cyclone. As shown in FIG. 2, when the radius of the cyclone is 5 cm, particles having diameters of 7 μm or smaller cannot be separated with a wind speed of 5 m/s. In order to separate particles having a diameter of 5 μm, the wind speed needs to be set to 10 m/s.
In general, it is difficult to change the diameter of the cyclone. Therefore, a wind speed higher than or equal to a predetermined level needs to be maintained in order to stably separate toner particles having diameters larger than or equal to a predetermined size. However, the suction blower in the cyclone separator generally requires a time to achieve a steady state during startup and shutdown. Accordingly, the wind speed in the sucking section of the cyclone is unstable during transition such as the startup and shutdown, and the fine particles of the toner cannot be separated as shown in FIG. 2. Thus, the toner is discharged to outside the apparatus and pollutes the exterior of the apparatus during the transition. Moreover, when a filter for collecting fine particles of toner is disposed in the air exhaust channel, excessive toner is carried to the filter, and shortens the lifetime of the filter.
In particular, when a toner collecting device of the cyclone separator type is used in an image forming apparatus, the suction blower is sometimes activated or shut down under abnormal conditions of the image forming apparatus, for example, shutdowns caused by paper jams or malfunctions.
This leads to early clogging of the filter for collecting the fine particles of the toner. Thus, an increase in costs for exchanging the filter and an increase in the size of the filter are unavoidable.